Session transfer in a communication network

ABSTRACT

A method and apparatus for transferring a session from a packet switched access network to a circuit switched access network. A Mobility Management Entity receives a service type indicator from a gateway node. The service type indicator indicates a type of service for the session, and is associated with bearers used for the session. The Mobility Management Entity subsequently receives, from an eNodeB, an indication that the session is to be transferred from the packet switched network to the circuit switched access network. The Mobility Management Entity determines the bearers associated with the session using the service type indicator, and initiates transfer of the session using those bearers. This ensures that the correct bearers are transferred regardless of whether or not identifiers such as QCI values have been ascribed to other types of service.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of pending U.S. application Ser. No.13/245,320, filed on Sep. 26, 2011, now U.S. Pat. No. 9,078,172 (IssuedJul. 7, 2015), which is a continuation of PCT/EP2010/064310, filed onSep. 28, 2010, the disclosures of which are hereby incorporated hereinby reference.

TECHNICAL HELD

The present invention relates to the field of session transfer in acommunication network.

BACKGROUND

Long Term Evolution (LTE) is a communication network technologycurrently under development by the 3rd Generation Partnership Project(3GPP). LTE requires a new radio access technique termed EvolvedUniversal Terrestrial Radio Access Network (E-UTRAN), which is designedto improve network capacity, reduce latency in the network, andconsequently improve the end-user's experience. System ArchitectureEvolution (SAE) is the core network architecture for LTE communicationnetworks.

LTE uses exclusively packet switched (PS) signalling. When a networkoperator wishes to introduce LTE, he will be unable to operate acomplete LTE service from the first day. LTE will need to be rolled outgradually to replace existing technologies. In order to do this, LTEnetworks must have some way of interacting with networks that use othertechnology, such as circuit switched (CS) signalling. Single Radio VoiceCall Continuity (SRVCC), described in 3GPP TS 23.237 and 3GPP TS 23.216,allows handover of a session from an LTE network to a CS network.

Referring to FIG. 1, there is illustrated a scenario in which a UserEquipment (UE) 1 has an established LTE bearer with ongoing speechsession over an IP Multimedia Subsystem (IMS) in a location 2 with LTEcoverage. The UE 1 then moves to a second location 3 in which LTEcoverage is no longer available, but a legacy CS network providescoverage. The LTE network communicates with a Mobile Switching Centre(MSC) Server 4 to indicate that the session is to be handed over fromthe LTE network to the CS network. The MSC server 4 notifies the IMSnetwork 5 of the handover. The IMS network then ensures that the sessioncan be handled by the CS network.

Similarly, handover can take place from UTRAN (HSPA) using IMS to a CSaccess. In the below description, the example of LTE is used, but can bereplaced with HSPA.

A problem arises when, for example, a video call is to be transferredfrom the LTE network to a PS network. The access network is not awarethat the call to be moved from PS to CS access is a video call, and sothe access network cannot identify a difference between bearers usedwhen setting up the call to carry video from a video call, or bearersused for other video applications, such as a video sharing applicationor a Mobile TV session.

One suggestion (described in 3GPP TR 23.886v0.3.1) for video call SRVCCassumes that the access network can determine that a video call istaking place by looking at the bearers that have been established. Eachbearer is assigned a Quality of Service Class Identifier (QCI) dependingon the type of media that is being transported by the bearer. If onebearer with QCI=1 (indicating voice) and another bearer with QCI=2(indicating video) exist, then it is assumed that the call is a videocall, and should be transferred as such.

A problem with this solution is that is restricts the usage of existingbearers. While QCI=2 is typically used for the video component of avideo call. QCI=2 can be used for other types of video, so requiringthat QCI=2 is only used for video calls creates problems with backwardcompatibility with existing terminals and applications that may useQCI=2 for video uses other than video calls. Furthermore, the describedin 3GPP TR 23.886v0.3.1 implies that only one bearer can use QCI=2. Thisis because video may be streamed using different applications, eachusing QCI=2, and there is no way of knowing from QCI=2 which bearerrelates to the video call.

A further problem is that operators may wish to use QCI values otherthan 2 for video calls. For example, a network operator might wish toreserve QCI=2 for mobile TV in the network. This would not be possiblein the solution described in 3GPP TR 23.886v0.3.1, as the detection of avideo call would wrongly assume that the mobile TV video relates to avideo call.

Note that this problem is not specific to video calls, but to any typeof session where more than one bearer is required for the session.

SUMMARY

According to a first aspect of the invention, there is provided a methodof transferring a session from a packet switched access network to acircuit switched access network. A Mobility Management Entity (MME)receives a service type indicator from a gateway node. The service typeindicator indicates a type of service for the session, and is associatedwith bearers used for the session. The MME subsequently receives, froman eNodeB, an indication that the session is to be transferred from thepacket switched network to the circuit switched access network. The MMEdetermines the bearers associated with the session using the servicetype indicator, and initiates transfer of the session using thosebearers. This ensures that the correct bearers are transferredregardless of whether or not identifiers such as QCI values have beenascribed to other types of service.

As an option, the MME sends to a Mobile Switching Centre (MSC) Server anindication of the type of service to a MSC Server. The indication of thetype of service allows the MSC to perform any of allocation of resourcesand invoking procedures relating to the type of service.

As a further option, the MME sends to a User Equipment (UE) involved inthe session an indication that Single Radio Voice Call Continuity forthe type of service has been invoked. In still a further option, the MMEsends to the UE involved in the session an indication of the bearersassociated with the session.

In an optional embodiment, prior to the MME receiving the service typeindicator from the gateway node, a Policy Charging and Rules Function(PCRF), initiates bearers for the session and determines a service type.It then determines the service type indicator using the determinedservice type and sends the service type indicator to the gateway nodefor forwarding to the MME.

The service type indicated by the service type indicator is optionallyselected from any of a video call, a voice call, a facsimile message, anIP Multimedia Subsystem priority message and circuit switched data,although it will be appreciated that it could be used to indicate anytype of service.

As an option, the packet switched network is selected from any of a LongTerm Evolution (LIE) or High Speed Packet Access (HSPA) network.

According to a second aspect, there is provided an MME for use in acommunication network. The MME is provided with a first receiver forreceiving from a gateway node a service type indicator, the service typeindicator indicating a type of service for a session handled by the MME,the service type indicator being associated with bearers used for thesession. A memory is provided for storing the received service typeindicator. A second receiver is provided for receiving from an eNodeB anindication that the session is to be transferred from a packet switchedaccess network to a circuit switched access network. A processor is alsoprovided for determining the bearers associated with the session usingthe service type indicator, and initiating transfer of the session usingthose bearers.

As an option, the MME is also provided with a first transmitter forsending to a MSC Server an indication of the type of service. Theindication of the type of service is usable by the MSC to performactions such as allocation of resources and invoking procedures relatingto the type of service.

As a further option, the MME is provided with a second transmitter forsending to a UE involved in the session an indication that Single RadioVoice Call Continuity for the type of service has been invoked and anindication of the bearers associated with the session.

According to a third aspect, there is provided a UE for use in acommunication network. The UE is capable of handling a transfer of anongoing session from a packet switched access network to a circuitswitched access network. The UE is provided with a receiver forreceiving from a MME a message relating to transfer of the ongoingsession from the packet switched access network to a circuit switchedaccess. The message includes an indication that Single Radio Voice CallContinuity for the type of service has been invoked, and an indicationof the bearers associated with the session, A processor is also providedfor determining further action on the basis of the indication thatSingle Radio Voice Call Continuity for the type of service has beeninvoked and the indication of the bearers associated with the session.

According to a third aspect, there is provided a PCRF node for use in acommunication network. The PCRF node is provided with a receiver forreceiving from a Call Session Control Function (CSCF) node a messagerelating to setting up or upgrading of a session. The message includesan indication of a type of service used in the session. A processor isprovided for setting up bearers for the session and generating a servicetype indicator for use in a subsequent session transfer from a packetswitched network to a circuit switched access network. A transmitter isalso provided for sending the service type indicator to a gateway nodefor subsequent forwarding to a MME.

According to a fourth aspect, there is provided a P-CSCF for use in acommunication network. The P-CSCF is provided with a processor fordetermining a type of service being used for a packet switched sessionand a transmitter for sending to a PCRF node a message, the messageincluding an indication of the type of service being used. Theindication of the type of service being used is subsequently usable inthe event of transfer of the session to a different access network.

According to a fifth aspect, there is provided a MSC Server for use in acommunication network. The MSC Server is provided with a receiver forreceiving from a MME an indication of a type of service being used for asession in the event that the session is being transferred from a packetswitched access network to a circuit switched access network. Aprocessor is also provided for, on the basis of the indication, eitherallocating resources for the session and invoking procedures for thesession.

According to a sixth aspect, there is provided a computer program,comprising computer readable code which, when run on a computer devicecauses the computer device to behave as any of a MME, UE, a PCRF node, aP-CSCF node and a MSC Server according as described in any of the secondto fifth aspects.

According to a seventh aspect, there is provided a computer programproduct comprising a computer readable medium and a computer program asdescribed above in the sixth aspect, wherein the computer program isstored on the computer readable medium.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates schematically in a block diagram a handover from anLTE network to a legacy CS network;

FIG. 2 is a signalling diagram illustrating procedures during callestablishment in an LTE network;

FIG. 3 is a signalling diagram illustrating procedures during handoverof a UE from an LTE network to a CS network;

FIG. 4 illustrates schematically in a block diagram a MobilityManagement Entity according to an embodiment of the invention;

FIG. 5 illustrates schematically in a block diagram User Equipmentaccording to an embodiment of the invention;

FIG. 6 illustrates schematically in a block diagram a Policy Chargingand Rules Function node according to an embodiment of the invention;

FIG. 7 illustrates schematically in a block diagram a MobilityProxy-Call Session Control Function according to an embodiment of theinvention; and

FIG. 8 illustrates schematically in a block diagram a Mobile SwitchingCentre Server according to an embodiment of the invention.

DETAILED DESCRIPTION

The invention avoids the problems associated with relying on QCI valuesto identify the service type by providing a service type indicator thatcan be used for access transfer when a session is transferred. Thefollowing description uses an example where the type of service is avideo call, although it will be appreciated that the invention can applyto other types of service, such as fax or CS data services.

Referring to FIG. 2 herein, when a UE 1 establishes a session (step S1)using an LTE network, a Proxy-Call Session Control Function (P-CSCF) 6in the IMS network determines the type of service that is being used.Note also that step S1 can be performed in the event that a service typeis changed during a session. For example, the same procedures apply whena voice call is upgraded to a video call.

In step S2, the P-CSCF communicates with a Policy Charging and RulesFunction (PCRF) 7 to ensure that access resources are set up for thesession. This includes setting up suitable bearers for the media beingsent during the session. The P-CSCF 6 may also indicate to the PCRF 7the service being used, for example by sending an IMS CommunicationService Identifier (ICSI). As an extension, the P-CSCF may also indicatewhat type of service is being used, for example a speech call, or avideo call. This gives the PCRF 7 more information in order that it candetermine how to handle the session, without requiring the PCRF tounderstand which ICSI maps to which service type. Note that there may bemore than one service may be available that can be used to establish avideo call, and any of these services should be capable of beingtransferred if a session moves from a PS to a CS access network.

In step S3, the PCRF 7 initiates the setting up of relevant bearers forthe session (e.g., a QCI=1 bearer for the speech part of the video calland a QCI=x bearer for the video part of the video call), by interactingwith the PDN Gateway (PGW) or Serving gateway (SGW) 8. The PCRF 7 alsoindicates to the PGW/SGW 8 that the session is related to a video callby sending a service type indicator to the PGW/SGW 8 indicating the typeof service, for example “service type=video call”. Examples of types ofservice that may be indicated include speech call, video call, CS data,IMS priority call or fax.

Note that in the event that the PCRF 7 only received the communicationservice used from the P-CSCF 6, the PCRF 7 will need to use a localpolicy to map the communication service to the service type anddetermine the relevant service type indicator.

In step S4, The PGW/SGW 8 interacts with a Mobility Management Entity(MME) 9 during the bearer allocation, as the MME is involved in thebearer activation/deactivation process. The MME is also responsible forselecting the SGW 8 and authenticating the UE and user by interactingwith a Home Subscriber Server (HSS) in the IMS network. The PGW/SGW 8sends the service type indicator to the MME 9. As a result, and for avideo call, the MME 9 considers the bearer related to QCI=1 and QCI=x tobe related to the service type indicator. In other words, if the servicetype indicator indicates that the session is a video call, the MME 9relates QCI=1 and QCI=x to the video call.

If there is no need to transfer the session between access networks forthe duration of the session, than the service type indicator will not beused. However, if there is a need to transfer the session from the LTEnetwork to a CS access network, then SRVCC is triggered, as illustratedin FIG. 3.

In step S5, an eNodeB 10 indicates to the MME 9 that the session is tobe transferred to a CS network and that SRVCC is required.

In step S6, the MME 9 has knowledge of the service type indicator forthe session subject to access transfer (for example, that it is a videocall), and the bearers associated with the service type indicator.Therefore the MME 9 handles the QCI=x bearer (for the video part of thevideo call) in the same way as it handles the QCI=1 bearer for PS accesstransfer and for suspend/resume cases during SRVCC, as described in 3GPPTS 23.216 v9.4.0. In this way, the session is identified as relating toa video call, but there is no need to use QCI=2 as proposed in TR.23.886 v.0.3.1 to identify the video part of the call, which allowsoperators more flexibility in assigning QCI values to video bearers.

In an optional embodiment, the MME 9 may decide not to execute theservice type specific SRVCC procedures and instead execute only normalSRVCC. In this case, the MME 9 may still handle the QCI=x bearer in thesame way as the QCI=1 bearer. This may occur where, for example, if anetwork operator does not wish to support the service type specificSRVCC procedures for this subscriber.

If configured to do so, the MME 9 indicates the type of service to theMSC Server 4 during the transfer. This may be done simply by forwardingthe service type indicator to the MSC Server 4. This allows the MSCServer 4 to allocate resources for the video call or to invokeprocedures specific to video calls. The MSC Server 4 performs therequired actions and confirms to the MME 4 whether the service typespecific SRVCC has been performed successfully, or whether only normalSRVCC has been performed. Normal SRVCC may be performed, for example, ifthe access used after the transfer does not support video call, e.g.,GERAN.

In a further embodiment of the invention, as illustrated in step S7, thenetwork (in other words, the MSC Server 4 and the MME 9) indicatestowards the UE 1 that SRVCC procedures for the specific service type isbeing executed, and an indication of the bearers associated with thesession. In situations in which the network may not be able to reliablyexecute video SRVCC, informing the UE 1 of the SRVCC procedures ensuresthat the UE 1 will not attempt to execute full video SRVCC procedures ina case where the network will not allow this. Such cases include, forexample, local policies or a temporary lack of resources.

Referring to FIG. 4, there is illustrated a MME 9. The MME 9 is providedwith a first receiver 11 for receiving the service type indicator fromthe PGW/SGW 8. As described above, the service type indicator indicatesthe type of service being used in the session handled by the MME 9 andis associated with bearers used for the session. A computer readablemedium in the form of a memory 12 is used to store the service typeindicator. In the event of the session being transferred from one accesstype to another, a second receiver 13 receives (from the eNodeB 10) anindication that the session is to be transferred. A processor 14 isprovided for determining the bearers associated with the session usingthe service type indicator, and initiating transfer of the session usingthose bearers.

The MME 9 may also be provided with a first transmitter 16 forcommunicating with the MSC Server 4 when it is required to send anindication of the type of service to the MSC Server in order to allowthe MSC Server 4 to allocate resources or invoke special procedures Asecond transmitter 17 may also be provided for informing the UE 1involved in the session that SRVCC for the type of service has beeninvoked and an indication of the bearers associated with the session.

The memory 12 may also be used to store a computer program 18 which,when run by the processor 14, causes the MME 9 to behave as describedabove.

Turning now to FIG. 5, there is illustrated a UE 1. The UE 1 is providedwith a receiver 19 for receiving a message relating to transfer of theongoing session from the packet switched access network to a circuitswitched access from the MME 9. The message includes an indication thatSRVCC for the type of service has been invoked and an indication of thebearers associated with the session. A processor 20 is also provided fordetermining further action on the basis of the indication that SRVCC forthe type of service has been invoked and the indication of the bearersassociated with the session.

A computer readable medium in the form of a memory 21 may also beprovided. This may be used to store a computer program 22 which, whenrun by the processor 20, cause the UE 1 to behave as described above.

FIG. 6 illustrates a PCRF 7. The PCRF 7 is provided with a receiver 23for receiving from a P-CSCF 6 a message relating to setting up orupgrading of a session. As described above, the message includes anindication of a type of service used in the session. A processor 24 isprovided for setting up or initializing bearers for the session anddetermining a service type indicator for use in a subsequent sessiontransfer from a packet switched network to a circuit switched accessnetwork. This determination may either be a generation of the servicetype indicator or it may have been received from the P-CSCF 6. Atransmitter 25 is provided for sending to the PGW/SGW 8 the service typeindicator for subsequent forwarding to the MME 9.

A computer readable medium in the form of a memory 25 may also beprovided. This may be used to store a computer program 26 which, whenrun by the processor 24, cause the PCRF 7 to behave as described above.

Referring to FIG. 7, there is illustrated a P-CSCF 6, which is providedwith a processor 29 for determining a type of service being used for apacket switched session. A transmitter 28 is provided for sending to amessage to the PCRF 7, the message including an indication of the typeof service being used.

A computer readable medium in the form of a memory 29 may also beprovided. This may be used to store a computer program 30 which, whenrun by the processor 27, cause the P-CSCF 6 to behave as describedabove.

FIG. 8 illustrates a MSC Server 4, which is provided with a receiver 31for receiving from an indication of a type of service being used for asession from the MME 9. A processor 32 is provided for, on the basis ofthe indication, allocating resources for the session and/or invokingprocedures for the session.

A computer readable medium in the form of a memory 33 may also beprovided. This may be used to store a computer program 34 which, whenrun by the processor 32, cause the MSC Server 4 to behave as describedabove.

By using the procedures described above, the correct bearers will betransferred during SRVCC procedures. Furthermore, a UE may use multiplebearers with some QCI value without risking that the “wrong” bearer istransferred during the transfer, or restricting the usage of bearer ofone type to only one. The procedures described above also allow thenetwork operator to decide on the QCI values used for video calls, whichgives sufficient flexibility to allow different operators to usedifferent QCI values for video, and also different QCI values fordifferent subscribers.

It will be appreciated by the person of skill in the art that variousmodifications may be made to the above-described embodiments withoutdeparting from the scope of the present invention as described in theappended claims. For example, the above description refers to a LTE PSnetwork, but the invention applies to other PS networks, for example aHigh Speed Packet Access (HSPA) network. Furthermore, the abovedescription assumes that the type service used in the session is a videocall. However, it will be appreciated that any type of service may beidentified. Examples of such services include IMS priority calls, voicecalls, CS data and fax messages.

The following abbreviations have been used in this specification:

-   3GPP 3rd Generation Partnership Project-   BSC Base Station Controller-   CS circuit switched-   E-UTRAN Evolved Universal Terrestrial Radio Access Network-   eNB eNodeB-   HSPA High Speed Packet Access-   ICSI IMS Communication Service Identifier-   IMS IP Multimedia Subsystem-   LTE Long Term Evolution-   MME Mobility Management Entity-   MSC Mobile Switching Centre-   P-CSCF Proxy-Call Session Control Function-   PCRF Policy Charging and Rules Function-   PGW PDN Gateway-   PS packet switched-   RAN Radio Access Network-   RNC Radio Network Controller-   SAE System Architecture Evolution-   SGW Serving Gateway-   SIP Session Initiation Protocol-   UE User Equipment-   UTRAN UMTS Terrestrial Radio Access Network

The invention claimed is:
 1. A Policy Charging and Rules Function nodefor use in a communication network, the Policy Charging and RulesFunction node comprising: a receiver for receiving from a Call SessionControl Function node a message relating to setting up or upgrading of asession, the message including an indication of a type of service usedin the session; a processor for setting up bearers for the session andgenerating a service type indicator for use in a subsequent sessiontransfer from a packet switched network to a circuit switched accessnetwork, wherein the service type indicator is associated with thebearers used for the session; and a transmitter for sending to a gatewaynode the service type indicator for subsequent forwarding to a MobilityManagement Entity.
 2. A Proxy-Call Session Control Function node for usein a communication network, the Proxy-Call Session Control Function nodecomprising: a processor for determining a type of service being used fora packet switched session; and a transmitter for sending to a PolicyCharging and Rules Function node a message, the message including anindication of the type of service being used, wherein the indication ofthe type of service being used is associated with bearers used for thepacket switched session.